This invention relates to an improved method for processing glass fiber reinforced thermoplastic resins and more particularly to an improved method for producing high impact molded or extruded parts from compositions comprising glass fiber and thermoplastic resin, and to a method for enhancing the impact properties of glass fiber reinforced thermoplastic resins.
Glass fiber reinforcement is added to a variety of plastic matricies to improve the strength, dimensional stability and heat resistance of the composite. The addition of reinforcing fibers in the form of chopped or milled glass strand to thermoplastic molding resins enhances stiffness, reduces creep and improves overall dimensional stability of molded parts, particularly at elevated temperatures. To be effective in molding resins the glass fiber surfaces normally must be treated with a coupling agent to improve adhesion between the fiber and the matrix resin, and a wide variety of silane compounds have been developed for this purpose. Glass fibers treated with appropriate coupling agents have been employed to reinforce a wide variety of thermoplastics including polyamide (nylon) and polypropylene. Where the matrix resin is crystalline as in nylon, for example, marked increases in flexural strength, rigidity and impact resistance are noted. However, in rigid amorphous molding resins such as polystyrene and styrene-acrylonitrile copolymers which are generally more brittle in character, the addition of chopped or milled glass fiber normally results only in an increase in rigidity, flexural modulus and tensile strength without improving the generally low impact strength of the matrix resin. These glass filled composites are thus more brittle and less ductile than the corresponding unfilled counterparts. An improved method for reinforcing such brittle amorphous resins which would result in both improved dimensional stability and increased impact strength and ductility would thus be a useful advance in the art.